Laser beams often do not have a uniform distribution of intensity throughout their cross section. This is true of a great many laser sources. The intensity distribution of many laser beams is described, for instance, by a bell shaped curve (Gaussian profile) which is rotationally symmetrical to the direction of spread of the beam. In the case of the so-called unstable resonators the intensity of the laser beam often is characterized by a hole in the middle of the beam cross section. Intensity peaks, so-called hot spots, frequently occur both with pulsed and continuous laser sources. These are limited areas in the beam cross section where the intensity of the laser beam is much greater than in the remainder of the area. Such hot spots either can appear at certain locations or they may jump within the cross section of the beam.
This irregular distribution of the beam intensity throughout the beam cross section and solid angle is disadvantageous for a variety of applications of laser beams. Irregular intensity distributions or intensity peaks and inhomogeneous or unsymmetrical angular energy distributions can be disturbing, for instance, when pieces of large area are to be illuminated or processed with the help of laser beams.
It is true that disturbing intensity peaks do not occur with transverse gas discharge lasers, such as TEA-CO.sub.2 lasers or excimer lasers, yet they must be manipulated optically to illuminate a piece which has a large surface area, and this means having to put up with considerable losses in intensity. Frequently also an adaptation of the angular energy distribution is required.
Known methods of homogenizing the distribution of intensity in laser beams are expensive and/or not applicable in all wavelength sections.
DE 38 29 728 A1 specifies a device for homogenizing the intensity distribution in the cross section of a laser beam with which optical elements, each accommodating part of the cross section of the laser beam, are disposed in said laser beam to mutually superimpose their respective partial beams. That is accomplished by so-called cylinder lens rods.
DE 38 41 045 A1 describes an arrangement for homogenizing the intensity distribution in the cross section of a laser beam, comprising a prism which is arranged in the resonator.
In the specification below, the prior art cited above will be assumed to be known.
Another difficulty sometimes encountered in laser applications is the fact that two partial beams must be provided which are separated in space and have the same angular energy distribution, each partial beam serving to illuminate an area of its own.